Table of Contents
What is a Network ?
A network connects devices to share resources and communicate. In a computer network, devices (also called nodes) can include things like computers, TVs, phones, and network infrastructure such as routers and switches. A resource is anything shared across the network, like webpages, shared printers, or cloud applications.
In short, a network links nodes to efficiently share resources.
Networking Devices
Clients and servers
In a network, clients and servers have different roles:
- A client requests a service.
- A server provides the service.
These roles can change depending on the situation. For example, a TV streaming content from Netflix is a client, while Netflix’s server is the server. Devices can switch roles, like two PCs sharing a file—one acting as the server and the other as the client.
Endpoints or end hosts refer to both clients and servers, with other devices in the network connecting them.
Example
Two desktop PCs sharing a file. The PC on the left is functioning as a client, and the PC on the right is functioning as a server.
Switches (Layer 2)
A switch connects devices within a Local Area Network (LAN), allowing them to communicate with each other.
Key points:
- Devices connect to the switch via ports (physical connectors).
- Switches have many ports (usually 24-48) to support multiple devices.
- A switch manages communication within a LAN but does not connect to external networks.
In essence, a switch acts as a central hub for devices to interact within a local network.
Example
Three end hosts connected to a switch
Routers (Layer 3)
A router connects a LAN to external networks like the internet, enabling communication beyond the local network.
Key points:
- Routers are placed at the edge of a LAN to connect it to other networks, including the internet.
- Unlike switches, which operate within a LAN, routers manage communication between LANs and external networks.
- Wireless routers combine a router, switch, access point, and firewall, serving small networks.
Simply put, while switches connect devices within a LAN, routers link LANs to external networks.
Example
Two LANs connected to the internet via a router at the edge of each LAN
Note
A cloud icon in a network diagram represents parts of the network that are not important or are unknown. For example, it’s often used to show the internet without detailing its complexity. In this case, we only need to know that the two LANs are connected to the internet.
Firewalls (Can operate at Layers 3, 4, and 7)
A firewall controls the traffic entering or leaving a network, either as hardware or software, and works based on pre-configured rules.
- Network firewalls filter traffic for the entire network.
- Host-based firewalls are installed on individual devices, filtering traffic specific to that device.
- Next-Generation Firewalls (NGFW) offer advanced filtering for enhanced security.
Firewalls protect networks by blocking harmful traffic and allowing safe communication based on set rules.
Example
A firewall between each LAN and the internet secures the network. Network communications between the two LANs are allowed, but malicious traffic from an attacker is denied.
Summary
- A Local Area Network (LAN) connects devices in a small area, like an office, while a Wide Area Network (WAN) spans large distances, such as between cities.
- Clients request services from servers, and servers provide those services. Depending on the task, devices can act as both clients and servers.
- Switches connect devices within a LAN, offering many ports for device connections.
- Routers connect LANs to external networks like the internet.
- A wireless router combines a router, switch, access point, and firewall into one device.
- Firewalls filter traffic to protect networks by blocking harmful content and allowing secure communication.